Added optional [tile] no_draw=<bool> to exclude images from a hex

This can be used in rare cases when a multi-hex rule requires that a [tile] be used for matching purposes but without getting the image(s) drawn on it.

src/terrain/builder.cpp

@@ -782,6 +782,8 @@ void terrain_builder::add_constraints(terrain_builder::constraint_set &constrain
 			item_string.begin(), item_string.end());
 
 
+	constraint.no_draw = cfg["no_draw"].to_bool(false);
+
 	add_images_from_config(constraint.images, cfg, false);
 }
 
@@ -1081,8 +1083,10 @@ void terrain_builder::apply_rule(const terrain_builder::building_rule &rule, con
 
 		tile& btile = tile_map_[tloc];
 
-		BOOST_FOREACH(const rule_image &img, constraint.images) {
-			btile.images.push_back(tile::rule_image_rand(&img, rand_seed));
+		if (!constraint.no_draw) {
+			BOOST_FOREACH(const rule_image &img, constraint.images) {
+				btile.images.push_back(tile::rule_image_rand(&img, rand_seed));
+			}
 		}
 
 		// Sets flags

src/terrain/builder.hpp

@@ -256,6 +256,7 @@ class terrain_builder
 			set_flag(),
 			no_flag(),
 			has_flag(),
+			no_draw(),
 			images()
 			{}
 
@@ -265,6 +266,7 @@ class terrain_builder
 			set_flag(),
 			no_flag(),
 			has_flag(),
+			no_draw(),
 			images()
 			{}
 
@@ -273,6 +275,10 @@ class terrain_builder
 		std::vector<std::string> set_flag;
 		std::vector<std::string> no_flag;
 		std::vector<std::string> has_flag;
+
+		/** Whether to actually draw the images onto this hex or not */
+		bool no_draw;
+
 		rule_imagelist images;
 	};